Method for preparing light calcium carbonate using dolomite

Abstract

This invention discloses a method for preparing lightweight calcium carbonate from dolomite, comprising the following steps: crushing, grinding, and calcining raw dolomite to obtain lightly calcined dolomite powder; subjecting the lightly calcined dolomite powder to acid leaching to obtain an acid leaching solution; adjusting the pH of the acid leaching solution to 12.3-12.6 with alkali, then introducing carbon dioxide to bring the pH to 7.6-8.4, followed by solid-liquid separation to obtain lightweight calcium carbonate. This invention, through calcination, acid leaching, and carbonation of dolomite, produces lightweight calcium carbonate that not only meets the requirements for precipitated calcium carbonate for plastics in the standard "General Industrial Depositional Calcium Carbonate," but also meets the requirements for calcium carbonate for rubber, coatings, and papermaking, thus possessing significant application value and broad prospects.

Description

Technical Field

[0001] This invention relates to the field of inorganic non-metallic functional material preparation, and in particular to a method for preparing lightweight calcium carbonate using dolomite. Background Technology

[0002] With the increase in global population, economic development, and urbanization, the plastics industry is continuously developing and its application areas are expanding, especially in packaging, construction, automotive, and electronics. Light calcium carbonate, as an important plastic additive, can meet the growing performance and environmental requirements of these industries. Particularly in developing countries, rapid economic growth and the gradual maturation of the plastics industry will drive the rapid growth of the light calcium carbonate market. In Asia, Africa, and Latin America, the application market for light calcium carbonate will experience explosive growth, especially in low-end plastic products, packaging materials, and building materials, where it will gradually become a major filler material.

[0003] Dolomite is a sedimentary carbonate rock, mainly composed of dolomite, a complex salt of magnesite (MgCO3) and calcite (CaCO3) in a 1:1 ratio, with the chemical formula CaCO3·MgCO3. It is often mixed with quartz, feldspar, calcite, and clay minerals. Dolomite is widely used in metallurgy, building materials, chemicals, agriculture, rubber, papermaking, and plastics industries. Methods for separating calcium and magnesium elements from dolomite mainly include carbonation, acid hydrolysis, and ammonium leaching. The carbonation method involves calcining dolomite to obtain lightly calcined dolomite, which is then digested with water to remove calcium from the lightly calcined dolomite. 2+ Mg 2+ The digested dolomite is converted into a mixed slurry of Ca(OH)₂ and Mg(OH)₂. This slurry is then carbonized with CO₂ gas, converting Ca(OH)₂ to CaCO₃ and Mg(OH)₂ to Mg(HCO₃)₂. The carbonized liquid is then filtered, yielding precipitated calcium carbonate (light calcium carbonate) as the filter residue and a Mg(HCO₃)₂ solution as the filtrate. Further purification of the light calcium carbonate yields a high-quality light calcium carbonate product. However, the carbonization process is complex and can easily lead to a decrease in product purity. The acid hydrolysis method utilizes the reaction of inorganic acids with dolomite (or calcined powder) to produce a solution containing calcium and magnesium. This solution is then treated with a precipitant to obtain magnesium hydroxide or magnesium carbonate. While this method effectively separates calcium and magnesium products, it requires large amounts of inorganic acids and magnesium precipitants, resulting in difficult wastewater treatment and high production costs. The ammonia leaching method primarily utilizes ammonium salts to extract the digested dolomite ash. After ammonia stripping, magnesium is precipitated using a precipitant.

[0004] The methods for separating calcium and magnesium from dolomite mentioned above all focus on the preparation and recovery of magnesium products, while insufficient attention is paid to the recovery and preparation of calcium products. In fact, calcium in dolomite can be used to produce light calcium carbonate, but dolomite is mainly used to produce primary products with low added value. How to effectively increase the added value of dolomite mineral resources and conduct deep processing to produce high-value-added products is an urgent problem to be solved. Summary of the Invention

[0005] In order to overcome the above-mentioned defects of the prior art, the purpose of this invention is to provide a method for preparing light calcium carbonate from dolomite, thereby solving the technical problem that the added value of calcium carbonate products prepared from the separation of calcium and magnesium from dolomite mineral resources is low.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing light calcium carbonate using dolomite, comprising the following steps:

[0008] The raw dolomite ore is crushed, ground, and calcined to obtain lightly calcined dolomite powder;

[0009] Lightly calcined dolomite powder is subjected to acid leaching to obtain an acid leaching solution;

[0010] The acid leaching solution was adjusted to pH 12.3-12.6 with alkali, and then carbon dioxide was introduced to pH 7.6-8.4. After solid-liquid separation, light calcium carbonate was obtained.

[0011] Preferably, the particle size of the lightly calcined dolomite powder is less than 0.150 mm.

[0012] Preferably, in the calcination step, the calcination temperature is 850~950℃ and the calcination time is 0.5~2 h.

[0013] Preferably, the step of acid leaching lightly calcined dolomite powder includes: preparing lightly calcined dolomite powder into a slurry to obtain lightly calcined dolomite slurry; adjusting the pH of the lightly calcined dolomite slurry to 0.6~1.4 using an acidic solution, stirring at 60~80℃ for 0.5~1 h, and obtaining an acid leaching solution after solid-liquid separation.

[0014] Preferably, the step of preparing lightly calcined dolomite powder into a slurry includes: mixing lightly calcined dolomite powder with water evenly, and then aging it for 0.5 to 12 hours to obtain lightly calcined dolomite slurry.

[0015] Preferably, the solid content of the lightly burned dolomite magma is 5-20 wt%.

[0016] Preferably, the concentration of the acidic solution is 0.5~6 mol / L; the acidic solution is at least one of hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, and phosphoric acid.

[0017] Preferably, the step of alkali conditioning the acid leaching solution includes: a first-stage alkali conditioning, a second-stage alkali conditioning, a third-stage alkali conditioning, and a fourth-stage alkali conditioning; wherein the pH of the first-stage alkali conditioning is 4.0~5.0; the pH of the second-stage alkali conditioning is 7.0~8.0; the pH of the third-stage alkali conditioning is 9.2~9.5; and the pH of the fourth-stage alkali conditioning is 12.3~12.6.

[0018] Preferably, in the step of introducing carbon dioxide, the alkali-treated slurry is stirred at a stirring rate of 600~800 r / min.

[0019] Preferably, after solid-liquid separation, the obtained solid is further subjected to washing and drying treatment.

[0020] The beneficial effects of this invention are:

[0021] 1. The present invention produces light calcium carbonate by calcining, acid leaching (phase transfer) and carbonation of dolomite. The resulting calcium carbonate not only meets the technical requirements of HG / T 2226-2019 "General Industrial Deposited Calcium Carbonate" for precipitated calcium carbonate used in plastics, but also meets the requirements for precipitated calcium carbonate used in rubber, coatings and papermaking. Therefore, it has great potential for widespread application and broad prospects.

[0022] 2. Compared with the traditional limestone preparation of calcium carbonate, this invention uses dolomite, which is cheaper, as the calcium source to prepare industrial precipitated calcium carbonate, which can effectively reduce raw material costs and provide a feasible route for high value-added dolomite products. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below.

[0024] Figure 1 This is a schematic diagram of a method for preparing lightweight calcium carbonate using dolomite according to the present invention.

[0025] Figure 2 This is a schematic diagram of a method for preparing light calcium carbonate using dolomite in an embodiment of the present invention. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] Please see Figure 1This invention provides a method for preparing light calcium carbonate from dolomite, comprising the following steps: crushing, grinding, and calcining the raw dolomite to obtain lightly calcined dolomite powder; subjecting the lightly calcined dolomite powder to acid leaching to obtain an acid leaching solution; adjusting the pH of the acid leaching solution to 12.3-12.6 with alkali, then introducing carbon dioxide to a pH of 7.6-8.4, and finally separating the solid and liquid to obtain light calcium carbonate.

[0028] Specifically, such as Figure 2 As shown in the figure, the method for preparing light calcium carbonate from dolomite provided in this embodiment of the invention includes the following steps:

[0029] (1) The raw dolomite is crushed and ground to obtain dolomite powder with a particle size of less than 0.15 mm.

[0030] (2) Calcining dolomite powder at 850~950℃ for 0.5~2 h yields lightly calcined dolomite powder.

[0031] (3) Mix lightly calcined dolomite powder with water evenly, and then age it for 0.5 to 12 hours to obtain a lightly calcined dolomite slurry with a solid content of 5 to 20 wt%.

[0032] (4) Adjust the pH of the lightly calcined dolomite magma to 0.6-1.4 using an acidic solution, and stir at 60-80℃ for 0.5-1h. After solid-liquid separation, an acid leachate is obtained. The concentration of the acidic solution is preferably 0.5-6 mol / L; the acidic solution is at least one of hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, and phosphoric acid.

[0033] (5) The acid leaching solution is subjected to a first-stage alkali adjustment, a second-stage alkali adjustment, a third-stage alkali adjustment and a fourth-stage alkali adjustment in sequence; wherein the pH of the first-stage alkali adjustment is 4.0~5.0; the pH of the second-stage alkali adjustment is 7.0~8.0; the pH of the third-stage alkali adjustment is 9.2~9.5; and the pH of the fourth-stage alkali adjustment is 12.3~12.6 to obtain the first slurry.

[0034] (6) Stir the first slurry at a rate of 600~800 r / min and introduce carbon dioxide into the first slurry to obtain a second slurry with a pH of 7.6~8.4.

[0035] (7) Light calcium carbonate is obtained by solid-liquid separation, hot water washing and drying of the second slurry.

[0036] The principle of this invention for preparing light calcium carbonate from dolomite through calcination, acid leaching, and carbonation is as follows:

[0037] First, dolomite is calcined to obtain lightly calcined dolomite powder containing calcium oxide and magnesium oxide; then, it is acid-leached to dissolve the dolomite in an acidic solution, and after filtration, a calcium-containing powder is obtained. 2+ Mg2+ Mn 2+ Fe 3+ The process involves using a plasma-enhanced acid leaching solution, adjusting the pH to 12.3-12.6 to remove impurities such as iron and manganese ions, resulting in a first slurry containing only Ca(OH)₂ and Mg(OH)₂. Finally, CO₂ gas is introduced to adjust the pH to 7.6-8.4, causing Ca(OH)₂ in the first slurry to precipitate as CaCO₃, and Mg(OH)₂ to soluble Mg(HCO₃)₂, thus achieving effective separation of calcium and magnesium ions. If the pH is too high and the CO₂ is insufficient to fully react with Mg(OH)₂ to form Mg(HCO₃)₂, some Mg(OH)₂ will remain in the product. Conversely, if the pH is too low, the CaCO₃ deposition volume will be too small, failing to meet the required specifications. Furthermore, prolonged CO₂ introduction may partially dissolve and convert CaCO₃ into Ca(HCO₃)₂, leading to a deficiency in the CaCO₃ content. 2+ Conversion rate decreased.

[0038] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below.

[0039] In the following examples and comparative examples, the main crystalline phase of the dolomite ore used is dolomite, and its chemical composition mainly includes the following components: CaO 31.85%, MgO 21.33%, SiO2 0.74%, Al2O3 0.17%, Fe2O3 0.09%.

[0040] Example 1

[0041] The raw dolomite ore was coarsely and finely crushed, then ground and classified to obtain dolomite powder with a particle size of less than 0.15 mm. The obtained dolomite powder was calcined in a muffle furnace at 900℃ for 0.5 hours to obtain lightly calcined dolomite powder. 11.2 g of the lightly calcined dolomite powder was weighed and mixed with deionized water at a solid content of 20%, stirred thoroughly in a room temperature water bath for 0.5 hours, and then allowed to stand for 2 hours to age, obtaining a lightly calcined dolomite slurry. The lightly calcined dolomite slurry was mixed with a 3 mol / L hydrochloric acid solution, the pH of the slurry was adjusted to 0.6-0.7, and stirred in a water bath at 80℃ for 0.5 hours. The mixture was then filtered while hot to obtain a Ca-containing... 2+ Mg 2+ Mn 2+ Fe 3+The acid leaching solution was prepared using plasma. The pH of the acid leaching solution was adjusted to 4.3 using a 4 mol / L NaOH solution, and after filtration, a first filtrate was obtained. The pH of the first filtrate was adjusted to 7.3, and after filtration, a second filtrate was obtained. The pH of the second filtrate was adjusted to 9.5, and after filtration, a third filtrate was obtained. Finally, the weakly alkaline third filtrate was adjusted to a pH of 12.5 to obtain a first slurry containing Ca(OH)₂ and Mg(OH)₂. The first slurry was transferred to a carbonation apparatus, and carbonation was carried out at room temperature with CO₂ gas introduced at a stirring rate of 750 r / min. The CO₂ gas was stopped after the pH of the slurry was controlled to drop to 7.7-7.8, yielding a second slurry. Finally, the second slurry was filtered, and the solution was washed 2-3 times with hot water during the filtration process. After drying, precipitated calcium carbonate (light calcium carbonate) was obtained.

[0042] Example 2

[0043] The raw dolomite ore was coarsely and finely crushed, then ground and classified to obtain dolomite powder with a particle size of less than 0.15 mm. The obtained dolomite powder was calcined in a muffle furnace at 850℃ for 1.5 hours to obtain lightly calcined dolomite powder. 11.2 g of the lightly calcined dolomite powder was weighed and mixed with deionized water at a solid content of 15%, stirred thoroughly in a room temperature water bath for 1 hour, and then allowed to stand for 4 hours to obtain a lightly calcined dolomite slurry. The lightly calcined dolomite slurry was mixed with a 3 mol / L hydrochloric acid solution to adjust the pH to 0.7-0.8, stirred in a water bath at 80℃ for 1 hour, and filtered while hot to obtain a Ca-containing... 2+ Mg 2+ Mn 2+ Fe 3+ Plasma acid leaching solution. The pH of the acid leaching solution was adjusted to 4.3 using a 4 mol / L NaOH solution, and after filtration, a first filtrate was obtained. The pH of the first filtrate was adjusted to 7.3, and after filtration, a second filtrate was obtained. The pH of the second filtrate was adjusted to 9.3, and after filtration, a third filtrate was obtained. Finally, the weakly alkaline third filtrate was adjusted to a pH of 12.5 to obtain a first slurry containing Ca(OH)₂ and Mg(OH)₂. The first slurry was transferred to a carbonation device, and carbonation was carried out at room temperature by introducing CO₂ gas at a stirring rate of 750 r / min. After controlling the pH of the slurry to drop to 7.6-7.7, the CO₂ gas was stopped to obtain a second slurry. Finally, the second slurry was filtered, and the slurry was washed with hot water 2-3 times during the filtration process. After drying, precipitated calcium carbonate (light calcium carbonate) was obtained.

[0044] Example 3

[0045] The raw dolomite ore was coarsely and finely crushed, then ground and classified to obtain dolomite powder with a particle size of less than 0.15 mm. The obtained dolomite powder was calcined in a muffle furnace at 850℃ for 1 hour to obtain lightly calcined dolomite powder. 11.2 g of the lightly calcined dolomite powder was weighed and mixed with deionized water at a solid content of 10%, stirred thoroughly in a room temperature water bath for 1.5 hours, and then allowed to stand for aging for 6 hours to obtain a lightly calcined dolomite slurry. The lightly calcined dolomite slurry was mixed with a 3 mol / L hydrochloric acid solution to adjust the pH to 0.9-1.0, stirred in a water bath at 60℃ for 0.5 hours, and filtered while hot to obtain a Ca-containing... 2+ Mg 2+ Mn 2 + Fe 3+ Plasma acid leaching solution. The pH of the acid leaching solution was adjusted to 4.6 using a 4 mol / L NaOH solution, and after filtration, a first filtrate was obtained. The pH of the first filtrate was adjusted to 7.8, and after filtration, a second filtrate was obtained. The pH of the second filtrate was adjusted to 9.2, and after filtration, a third filtrate was obtained. Finally, the weakly alkaline third filtrate was adjusted to a pH of 12.3 to obtain a first slurry containing Ca(OH)₂ and Mg(OH)₂. The first slurry was transferred to a carbonation device, and carbonation was carried out at room temperature by introducing CO₂ gas at a stirring rate of 700 r / min. The CO₂ gas was stopped after the pH of the slurry was controlled to drop to 7.9-8.0 to obtain a second slurry. Finally, the second slurry was filtered, and the slurry was washed with hot water 2-3 times during the filtration process. After drying, precipitated calcium carbonate (light calcium carbonate) was obtained.

[0046] Example 4

[0047] The raw dolomite ore was coarsely and finely crushed, then ground and classified to obtain dolomite powder with a particle size of less than 0.15 mm. The obtained dolomite powder was calcined in a muffle furnace at 950℃ for 1 hour to obtain lightly calcined dolomite powder. 11.2 g of the lightly calcined dolomite powder was weighed and mixed with deionized water at a solid content of 15%, stirred thoroughly in a room temperature water bath for 2 hours, and then allowed to stand for aging for 8 hours to obtain a lightly calcined dolomite slurry. The lightly calcined dolomite slurry was mixed with a 3 mol / L hydrochloric acid solution, the pH of the slurry was adjusted to 0.8-0.9, and stirred in a water bath at 80℃ for 1 hour. The mixture was then filtered while hot to obtain a Ca-containing... 2+ Mg 2+ Mn 2+ Fe 3+The acid leaching solution was prepared using plasma. The pH of the acid leaching solution was adjusted to 4.7 using a 4 mol / L NaOH solution, and after filtration, a first filtrate was obtained. The pH of the first filtrate was adjusted to 7.8, and after filtration, a second filtrate was obtained. The pH of the second filtrate was adjusted to 9.4, and after filtration, a third filtrate was obtained. Finally, the weakly alkaline third filtrate was adjusted to a pH of 12.4 to obtain a first slurry containing Ca(OH)₂ and Mg(OH)₂. The first slurry was transferred to a carbonation apparatus, and carbonation was carried out at room temperature with CO₂ gas introduced at a stirring rate of 700 r / min. The CO₂ gas was stopped after the pH of the slurry was controlled to drop to 7.7-7.8, yielding a second slurry. Finally, the second slurry was filtered, and the solution was washed 2-3 times with hot water during filtration. After drying, precipitated calcium carbonate (light calcium carbonate) was obtained.

[0048] Example 5

[0049] The raw dolomite ore was coarsely and finely crushed, then ground and classified to obtain dolomite powder with a particle size of less than 0.15 mm. The obtained dolomite powder was calcined in a muffle furnace at 850℃ for 2 hours to obtain lightly calcined dolomite powder. 11.2 g of the lightly calcined dolomite powder was weighed and mixed with deionized water at a solid content of 10%, stirred thoroughly in a room temperature water bath for 2 hours, and then allowed to stand for 10 hours to obtain a lightly calcined dolomite slurry. The lightly calcined dolomite slurry was mixed with a 3 mol / L hydrochloric acid solution to adjust the pH to 1.0-1.1, stirred in a water bath at 70℃ for 1 hour, and filtered while hot to obtain a Ca-containing... 2+ Mg 2+ Mn 2+ Fe 3+ Plasma acid leaching solution. The pH of the acid leaching solution was adjusted to 4.4 using a 4 mol / L NaOH solution, and after filtration, a first filtrate was obtained. The pH of the first filtrate was adjusted to 7.6, and after filtration, a second filtrate was obtained. The pH of the second filtrate was adjusted to 9.3, and after filtration, a third filtrate was obtained. Finally, the weakly alkaline third filtrate was adjusted to a pH of 12.4 to obtain a first slurry containing Ca(OH)₂ and Mg(OH)₂. The first slurry was transferred to a carbonation device, and carbonation was carried out at room temperature by introducing CO₂ gas at a stirring rate of 700 r / min. After controlling the pH of the slurry to drop to 8.1-8.2, the CO₂ gas was stopped to obtain a second slurry. Finally, the second slurry was filtered, and the slurry was washed with hot water 2-3 times during the filtration process. After drying, precipitated calcium carbonate (light calcium carbonate) was obtained.

[0050] Example 6

[0051] The raw dolomite ore was coarsely and finely crushed, then ground and classified to obtain dolomite powder with a particle size of less than 0.15 mm. The obtained dolomite powder was calcined in a muffle furnace at 850℃ for 1 hour to obtain lightly calcined dolomite powder. 11.2 g of the lightly calcined dolomite powder was weighed and mixed with deionized water at a solid content of 5%, stirred thoroughly in a room temperature water bath for 2 hours, and then allowed to stand for 12 hours to obtain a lightly calcined dolomite slurry. The lightly calcined dolomite slurry was mixed with a 3 mol / L hydrochloric acid solution to adjust the pH to 1.3-1.4, stirred in a water bath at 80℃ for 1 hour, and filtered while hot to obtain a Ca-containing... 2+ Mg 2+ Mn 2+ Fe 3+ The acid leaching solution was prepared using plasma. The pH of the acid leaching solution was adjusted to 4.5 using a 4 mol / L NaOH solution, and after filtration, a first filtrate was obtained. The pH of the first filtrate was adjusted to 7.7, and after filtration, a second filtrate was obtained. The pH of the second filtrate was adjusted to 9.3, and after filtration, a third filtrate was obtained. Finally, the weakly alkaline third filtrate was adjusted to a pH of 12.4 to obtain a first slurry containing Ca(OH)₂ and Mg(OH)₂. The first slurry was transferred to a carbonation apparatus, and carbonation was carried out at room temperature with CO₂ gas introduced at a stirring rate of 750 r / min. The CO₂ gas was stopped when the pH of the slurry dropped to 8.3-8.4, yielding a second slurry. Finally, the second slurry was filtered, and the slurry was washed 2-3 times with hot water during the filtration process. After drying, precipitated calcium carbonate (light calcium carbonate) was obtained.

[0052] Example 7

[0053] Compared with Example 1, the dosage and preparation method of each reagent in Example 7 are basically the same. The difference is that in the acid leaching step, the lightly calcined dolomite slurry is mixed with hydrochloric acid without high-temperature water bath stirring. Instead, the lightly calcined dolomite slurry is mixed with a 3 mol / L hydrochloric acid solution, the pH of the slurry is adjusted to 0.6~0.7, and the acid leaching solution is obtained after filtration.

[0054] Example 8

[0055] Compared with Example 1, the dosage and preparation method of each reagent in Example 8 are basically the same. The difference is that the step of alkali adjustment of the acid leaching solution includes three stages of alkali adjustment, namely, adjusting the pH of the acid leaching solution to 7.3, filtering to obtain the first filtrate; adjusting the pH of the first filtrate to 9.5, filtering to obtain the second filtrate; and finally adjusting the pH of the second filtrate to 12.5 to obtain the first slurry.

[0056] Comparative Example 1

[0057] Compared with Example 1, the dosage and preparation method of each reagent in Comparative Example 1 are basically the same. The difference is that the step of alkali adjustment of the acid leaching solution is a single-stage alkali adjustment, that is, the acid leaching solution is directly adjusted to pH 12.5 to obtain the first slurry.

[0058] Comparative Example 2

[0059] Compared with Example 1, the dosage and preparation method of each reagent in Comparative Example 2 are basically the same. The difference is that in the step of alkali adjustment of the acid leaching solution, the pH of the fourth alkali adjustment is 12.0, that is, the first slurry with pH 12.0 is obtained.

[0060] Comparative Example 3

[0061] Compared with Example 1, the dosage and preparation method of each reagent in Comparative Example 3 are basically the same. The difference is that in the step of alkali adjustment of the acid leaching solution, the pH of the fourth alkali adjustment is 12.2, that is, the first slurry with pH 12.2 is obtained.

[0062] Comparative Example 4

[0063] Compared with Example 1, the dosage and preparation method of each reagent in Comparative Example 4 are basically the same. The difference is that carbon dioxide is introduced into the first slurry, and the pH of the slurry is controlled to drop to 7.0~7.4 before the CO2 gas is stopped to obtain the second slurry, that is, the pH of the second slurry is 7.0~7.4.

[0064] The precipitated calcium carbonate prepared in Examples 1-8 and Comparative Examples 1-4 were subjected to performance tests, and the results are shown in Table 1.

[0065] Table 1

[0066]

[0067] As can be seen from the data in Table 1, the precipitated calcium carbonate (light calcium carbonate) prepared in the embodiments of the present invention exhibits excellent performance and meets the technical requirements for precipitated calcium carbonate for plastics in HG / T 2226-2019 "General Industrial Deposited Calcium Carbonate". Specifically, compared with Example 1, Example 7 shows that the lack of heating and stirring during the acid leaching process resulted in insufficient reaction between the hydrochloric acid and the calcined powder, thus causing Ca... 2+ The leaching rate is low. Compared with Comparative Example 1, Example 8 does not use multi-stage alkali adjustment or only uses two-stage alkali adjustment, which will result in slightly lower whiteness and higher iron and manganese content in the prepared calcium carbonate, or fail to meet the standard. This shows that using multi-stage pH-controlled alkali adjustment will effectively reduce the iron and manganese ion content, so that when the final product meets other index requirements, the whiteness is about 95 or above.

[0068] Compared to Example 1, Comparative Examples 2-3 involved multiple pH adjustments until the pH of the first slurry was less than 12.3, resulting in increased Ca content.2+ The conversion rate was low, meaning that less calcium carbonate was obtained. This was because after CO2 was introduced into the first slurry at this pH environment, the OH groups in the slurry... - HCO3 formed from CO2 - First with Mg 2+ The combination to form soluble Mg(HCO3)2 consumes a large amount of OH. - This results in insufficient OH- - It continues to react with CO2 to produce substances that can react with Ca. 2+ CO3 combines to form CaCO3 2- This affects Ca 2+ Conversion rate.

[0069] Compared to Example 1, Comparative Example 4 had a final carbonization pH closer to 7.0, resulting in a slightly lower CaCO3 deposition volume, and Ca... 2+ The conversion rate decreased because the CO2 introduction time was too long, which caused some of the CaCO3 in the slurry to dissolve and convert into Ca(HCO3)2, resulting in a decrease in Ca2+ concentration. 2+ As the conversion rate decreases, the particle size of CaCO3 decreases, thus affecting its settling volume.

[0070] In summary, the present invention uses dolomite as a calcium source and prepares precipitated calcium carbonate (light calcium carbonate) through calcination, acid leaching (phase transfer), and carbonation. The precipitated calcium carbonate meets the technical requirements for plastics in HG / T 2226-2019 "General Industrial Deposited Calcium Carbonate", and also meets the requirements for precipitated calcium carbonate for rubber, coatings, and papermaking in the same standard.

[0071] It should be noted that all the above embodiments belong to the same inventive concept, and the descriptions of each embodiment have different focuses. Where the description in a particular embodiment is not detailed, please refer to the description in other embodiments.

[0072] The embodiments described above are merely illustrative of implementation methods of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing lightweight calcium carbonate using dolomite, characterized in that, Includes the following steps: The raw dolomite ore is crushed, ground, and calcined to obtain lightly calcined dolomite powder; The lightly calcined dolomite powder was subjected to acid leaching to obtain an acid leaching solution; The acid leaching solution was adjusted to pH 12.3-12.6 with alkali, and then carbon dioxide was introduced to pH 7.6-8.

4. After solid-liquid separation, light calcium carbonate was obtained. In the calcination process, the calcination temperature is 850~950℃ and the calcination time is 0.5~2 h. The step of acid leaching the lightly calcined dolomite powder includes: The lightly calcined dolomite powder is slurried to obtain lightly calcined dolomite slurry; The pH of the lightly calcined dolomite magma was adjusted to 0.6-1.4 using an acidic solution, and stirred at 60-80°C for 0.5-1 h. After solid-liquid separation, an acid leaching solution was obtained. The step of alkali conditioning the acid leaching solution includes: a first-stage alkali conditioning, a second-stage alkali conditioning, a third-stage alkali conditioning, and a fourth-stage alkali conditioning; The pH of the alkaline adjustment section is 4.0~5.0; The pH of the two-stage alkali adjustment is 7.0~8.0; The pH of the three-stage alkali adjustment is 9.2~9.5; The pH of the four alkaline-adjusted sections is 12.3 to 12.

6.

2. The method for preparing light calcium carbonate from dolomite according to claim 1, characterized in that, The lightly calcined dolomite powder has a particle size of less than 0.150 mm.

3. The method for preparing light calcium carbonate from dolomite according to claim 1, characterized in that, The step of preparing the lightly calcined dolomite powder into a slurry includes: mixing the lightly calcined dolomite powder with water evenly, and then aging it for 0.5 to 12 hours to obtain a lightly calcined dolomite slurry.

4. The method for preparing light calcium carbonate from dolomite according to claim 1, characterized in that, The solid content of the lightly burned dolomite magma is 5-20 wt%.

5. The method for preparing lightweight calcium carbonate from dolomite according to claim 1, characterized in that, The concentration of the acidic solution is 0.5~6 mol / L; the acidic solution is at least one of hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, and phosphoric acid.

6. The method for preparing light calcium carbonate from dolomite according to claim 1, characterized in that, In the step of introducing carbon dioxide, the alkali-treated slurry is stirred at a stirring rate of 600~800 r / min.

7. The method for preparing light calcium carbonate from dolomite according to claim 1, characterized in that, After the solid-liquid separation is completed, the obtained solid is further subjected to washing and drying processes.

Images